[ft-announce] Re: [ft] [Freetype2] About Unpatent-Hinting

[David Turner]

> First,
> 
> I wonder if it is true that I can avoid the patent matter by using these
> define-options;
> 
> #define TT_CONFIG_OPTION_BYTECODE_INTERPRETER
> 
> #define TT_CONFIG_OPTION_UNPATENTED_HINTING................ in
> src.ftoption.h.
>
Yes, if you do that, you will compile a version of the bytecode interpreter
that will not execute any of the patented operations. The downside is that
for nearly all fonts, this will produce garbage output.

Which is why, since 2.3.0, doing this will use the auto-hinter anyway.
If you don't want that, compile your library without the auto-hinter module.
 
>  
> 
> Second,
> 
> I couldn't clearly understand when I look at the source code how
> unpainted_hinting can avoid the Patent issue.
> 
> Could you explain more in detail?
>
I won't go into long details here, it's pretty boring stuff. Essentially
the two earlier Apple patents cover a technique used to properly move points
along a diagonal to respect hinted widths, as well as pixel-precise adjustments
to the distorted outlines to deal with unescapable ill-cases.

There is also a third, later patent, that protects against the use of
approximations to the computations described in the first patent. It seems
someone at Apple realized that you could perfectly use approximated vector
outlines but still get some pretty decent results after rasterization.

the third patent isn't really dangerous to us. The two initial patents expire
on October 2009.

For more details, read the patent descriptions and the TrueType spec.
>  
> 
> Lastly, I want to know what types of roles does "Delta Instruction" play
> and what does it stand for?
> 
It's an instruction of the TrueType Virtual Machine. You should read the 
specification
to learn all the details.

Hope this helps,

- David Turner
- The FreeType Project  (www.freetype.org)


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> 
> It will be very helpful if you could answer me.
> 
> Thank you.
> 
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> 
> Best wishes
> 
> Hamish woo. 
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